Skip to content

Latest commit

 

History

History
38 lines (26 loc) · 2.79 KB

particle jammed soft finger building manual.md

File metadata and controls

38 lines (26 loc) · 2.79 KB
Raw

How to build a particle jammed soft finger

Many things can go wrong when you are trying to make a particle jammed soft finger. Here is a manual with procedures and some tips!

1. 3D print the skeleton

3D print the skeleton from the CAD model. Leave some holes on skeleton for inserting the tubes. Be aware that depending on the printer you use, there might be hollow structures in the finger which will cause problems for airtightness later.

2. 3D print the molds

We need molds for the silica gel shell and a skeleton mold to make space for the skeleton and joints inside the shell.

3. Build silica gel shell

  • Clean the remaining silica gel on molds
  • Spray mold-releasing oil on the inner part of molds contacting the gel
  • Put the finger skeleton mold inside the finger shell mold, clamp the molds and keep it steady
  • Measure 30mL ECOFLEX 0030 liquid A and 30mL liquid B, mix A and B in a cup, stir for 2 min
  • Put the stirred mixed liquid in a vacuum container. Start the compressor vacuum pump. When there is no bubbles generating in the liquid, turn off the pump. Gently remove the tube or lid and let the air in, in case the cup tips over
  • Slowly pour the bubble-free liquid into the clamped mold
  • Wait for 2 hours to demould

4. Add air tubes to the skeleton

Put a tiny piece of cloth into the end of tubes to prevent the ground coffee from being sucked in. Insert the air tubes into the holes on skeleton. Use super glue to fix the tubes in skeletons. Be careful not to block the tube.

5. Assemble the skeleton and shell

  • Cut silica gel scrap into small rectangles. Cut the rectangle gel in the center. Put them on the middle of skeletons as silica gel rings. The rings will increase the friction between shell and skeletons, and prevent the ground coffee from moving between different finger joints.
  • Cut the silica gel shell open at each joints. Tuck the skeletons into the shell while leaving the tubes outside.
  • Fill each joints with as much ground coffee as possible. Move the skeletons a bit to let the ground coffee fill every corner inside the joints.
  • Seal the silica gel shell. Pay attention to the place where tubes go out. Check the airtightness of finger primarily.
  • Connect the three small tubes from finger to a larger tube which will be connected to the vacuum regulator.

6. Airtightness checking

Apply soap water to the possible leaking area. Use syringe to slowly pump air in. Observe closely if there are bubbles anywhere.

If you cannot locate the leaking spot using soap water, soak the finger into a water tank while slowly pumping air in. Observe closely if there are bubbles anywhere.

Be aware that the junctions of different size tubes is highly probably leaky. The most reliable way is to seal the junctions and possibly the whole finger again using silica gel.